1. Field of the Invention
The present invention relates to improvement in a capacitor charging device including a flyback DC/DC converter and a strobe charging device for a camera.
2. Description of the Related Art
Japanese Patent Laid-Open No. 8-008089 discloses a configuration for detecting a malfunction of a circuit provided to a strobe device. In this configuration, a timer is started at the beginning of a step-up operation, a charging voltage after predetermined time is stored, and then a battery is checked. If the charge level is low regardless of enough power of battery, the charge step-up operation is stopped and warning is given.
In the above-described known art, however, predetermined time is necessary in order to detect a circuit malfunction of a forward DC/DC converter. Therefore, detection of the circuit malfunction is disadvantageously delayed by the predetermined time.
An object of the present invention it to provide a capacitor charging device and a strobe charging device for a camera, in which the number of components does not increase and a circuit malfunction can be detected just after charging is started.
According to an aspect of the present invention, a strobe charging device comprises: a light-emitting tube; a main capacitor for accumulating energy and for supplying the energy to the light-emitting tube; a transformer circuit which includes primary and secondary coils in order to accumulate the energy of a power supply in the main capacitor; a control circuit for controlling a current flowing from the power supply to the primary coil; a current detection circuit for detecting a current flowing through the secondary coil; and a determination circuit for determining the operation state of the device based on a detection result generated by the current detection circuit. The primary coil is connected to the power supply and the secondary coil is connected to the main capacitor. Also, a current starts to flow through the secondary coil after the control circuit stops a current flowing through the primary coil.
According to another aspect of the present invention, a strobe charging device comprises: a light-emitting tube; a main capacitor for accumulating energy and for supplying the energy to the light-emitting tube; a transformer circuit which includes primary and secondary coils in order to accumulate the energy of a power supply in the main capacitor; a control circuit for controlling a current flowing from the power supply to the primary coil; a current detection circuit for detecting a current flowing through the secondary coil; a time measuring circuit for measuring the time from when the control circuit stops a current flowing through the primary coil until the current detection circuit detects that the current flowing through the secondary coil reaches a predetermined level or until the current flowing through the secondary coil stops; a voltage detecting circuit for detecting the voltage of the main capacitor; and a determination circuit for determining the operation state of the device based on the measurement result generated by the time measuring circuit and on a voltage detected by the voltage detecting circuit. The primary coil is connected to the power supply and the secondary coil is connected to the main capacitor. Also, a current starts to flow through the secondary coil after the control circuit stops a current flowing through the primary coil.
Preferably, the determination circuit determines the operation state of the device based on a time corresponding to the voltage detected by the voltage detecting circuit and on the time measured by the time measuring circuit.